The research proposed herein seeks to determine the molecular level details of nitrogenase turnover, substrate binding, substrate reduction and metal cluster synthesis and insertion. The major approach is to construct, express and purify site-directed mutant and other variants of the Fe and MoFe proteins of nitrogenase. These purified proteins will then be characterized by X-ray crystallography, by biochemical and kinetic studies and by a variety of spectroscopic techniques. These experiments are designed to determine the chemical, redox and physical properties of each component of the Fe and MoFe proteins and how they interact with each other. The information obtained will be invaluable in attempts to enhance biological nitrogen fixation or to duplicate it synthetically. Increased fixed nitrogen equates to increased protein supply, which is a significant factor in good nutrition and health. In addition, the knowledge gained here is expected to greatly increase our understanding of a variety of fundamentally important processes like nucleotide controlled energy transduction, long range electron and proton transfer, and metal cluster insertion.